It’s hard to imagine how the essentially chemically inert gaseous elements could improve athletic performance. But xenon is surprisingly bioactive and can enhance the oxygen-carrying capacity of blood. Argon is thought to work the same way.

Xenon is known to interact with protein receptors and ion channels and function as a hypoxia-inducible factor (HIF), similar to nitrous oxide (laughing gas). As such, xenon has been used as an anesthetic for decades, notably in Russia.

When it comes to improving athletic performance, xenon is one of several agents known to activate production of HIF-1α, a protein alarm that triggers other proteins to come to the rescue of tissues deprived of oxygen. One of those secondary proteins is erythropoietin (EPO), a hormone that encourages the formation of red blood cells. Synthetic EPO is used for treating anemia in patients with cancer and kidney disease, but it is infamous as a banned performance-enhancing drug, especially among endurance athletes such as cyclists.

Athletes have turned to inhaling xenon in the same way they might train in low-oxygen conditions at high altitude. Xenon and argon clear from the body within hours, but the performance-enhancing effects can last several days. The agency did not announce how it would test for xenon or argon doping, which may be hard to detect beyond measuring variable HIF-1α or EPO levels.